An organic light emitting diode (OLED), as a current-mode light-emitting device, has been more and more widely adopted in the field of display due to its characteristics such as self-luminous property, fast response, wide view angle and capability of being fabricated on a flexible substrate.
When an OLED device emits light, the current for driving all pixels is supplied from a backplane power supply. However, wire for the backplane power supply has a certain resistance, and therefore, power voltage applied to an area proximal to the location of the power supply is higher than that applied to an area distal to the location of the power supply. This phenomenon is known as IR drop, the larger the size of an OLED display, the more significant the phenomenon. In addition, each pixel circuit has a set of thin-film transistors (TFTs) and storage capacitors integrated therein, and the current flowing through an OLED is not only controlled by a data voltage, but also affected by a threshold voltage of the TFT. Since it is not possible for TFTs in a plurality of pixel circuits to have an identical property, difference exists between threshold voltages of TFTs in various pixel circuits, which thus leads to difference in current flowing through OLED device, and further has an effect on uniformity of brightness over a display screen.